Do magnetars emit audible LW AM radio waves that can be heard on receivers?

On Jul 14, 4:11 pm, "George Dishman" wrote:

The relevant maths is:

http://www.sosmath.com/trig/prodform/prodform.html


The above link says nothing about amplitude-modulation

Radium wrote:

On Jul 13, 2:15 pm, wrote:
In rec.radio.amateur.space Radium wrote:

Hi:
Do magnetars emit AM radio waves below the medium-wave range? If so,
how do we detect these waves? Can these waves be heard on the AM
radio? If so, what do they sound like?

Frequencies above approximately 100 MHz almost always get through
the ionization layers.

Frequencies in the approximate range of 10 MHz to 100 MHz sometimes
get through

Frequencies below approximately 10 MHz almost never get through.

So, if by "the AM radio" you mean a Broadcast Band radio which
runs from about .5 MHz to 1.2 MHz, not a chance in hell of ever
hearing anything from off the planet.

Try again.

Okay. But what if this is a supercooled AM radio receiver on a
spaceship orbiting Earth? If I am on a space station like MIR and this
station has a supercooled AM radio 44.1 KHz frequency receiver, will I
hear anything specific of magnetars?

Nothing "specific". Thats the whole point. What exactly did you
hope to hear that you think is significant? Obviously you have
something in mind.
KLM



44.1 KHz is the carrier-frequency this hypothetical receiver receives.

I place the frequency of this hypothetical AM radio carrier wave at
44.1 KHz for the same reason CDs use a sample rate of 44.1 KHz -- it
is the minimum required to prevent aliasing.

AFAIK, space station orbit earth above the ionosphere so the
limitations [preventing long-waves from outer space from reaching the
Earth's surface] do not apply.

wrote in message
news
In rec.radio.amateur.space Chris L Peterson
wrote:
On Sun, 15 Jul 2007 03:45:01 GMT, wrote:

Spread spectrum technology uses discrete frequency hopping, not a
broad band signal as a carrier.

That is correct, it is a narrow band carrier which
moves.

That's one spread spectrum method. Not the only one. But regardless, it
still presents as a broad band carrier.

Nope, all spread spectrum is based on discrete frequencies with
frequency hopping of some sort.

Not always, consider the use of a frequency-shifted
fast PRBS as the carrier. Of course it is more
usual to use the PRBS to define the hop sequence in
the style you describe above but as you say your
background is communications, I'm sure you are aware
of the relationships between hop rate and carrier
spacing which lead to a band-limited white spectrum.

AM is a variation in amplitude of some signal- any signal- with time.

Nope, mathematically AM is defined as a single carrier frequency
multipled by the modulation frequency. That you get a variation in
amplitude is an effect, not a definition.

It is a bit of a stretch to call a signal comprised of every frequency
over a 100 GHz span AM.

Consider applying audio (with a DC bias) to a light
bulb and receiving it with a photocell. The carrier
is much more than 100 GHz wide, but I would still
call that AM, YMMV.

I'm afraid my background IS communications ...

Mine too ;-)

George

"Radium" wrote in message
ps.com...
On Jul 14, 4:11 pm, "George Dishman" wrote:

The relevant maths is:

http://www.sosmath.com/trig/prodform/prodform.html


The above link says nothing about amplitude-modulation

It says:

sin(a)sin(b) = 1/2 * [ cos(a-b) - cos(a+b) ]

Take a carrier at frequency fc:

Vc = sin(2*pi*fc*t)

and a typical modulating signal at fm:

Vm = sin(2*pi*fm*t)

Amplitude modulation involves multiplying those
together with an offset so that there is always
some level of carrier so the transmitted signal
is:

Vt = Vc * (1 + M * Vm)

where 0 M 1

You get components at cos(2*pi*(fc-fm)*t) and
cos(2*pi*(fc+fm)*t) as well as the carrier at fc.

George

"Radium" wrote in message
oups.com...
On Jul 14, 4:11 pm, "George Dishman" wrote:

Look at the maths, it is never wrong. Modulating fc
with fm gives a lowest frequency of fc-fm so as long
as fc fm, you don't get aliasing.

So an fm of 10 KHz would work on an fc of 10 KHz?

fc fm means fc should be greater than fm, not the same.
For fm = 10,000Hz and fc = 10,001Hz you get a lower
sideband at 1Hz and an upper sideband at 20,001Hz.

If you modulate 10kHz with 10Khz, the lower sideband
becomes 0Hz or DC. The value of that depends on the
phase of the modulating signal relative to the carrier
(which is now constant since they are at the same
frequency). Of course sending DC to an antenna won't
give you a transmitted signal but it doesn't produce
an alias either.

If you modulate 10,000Hz with 10,001Hz then your lower
sideband becomes -1Hz, and of course sin(-x) = sin(x)
so that is identical to a frequency of 1Hz which you
would get if you modulated with 9,999Hz. That ambiguity
is why we call such a signal an "alias", the 10,001Hz
signal appears after modulation then demodulation
masquerading as a signal of 9,999Hz.

George

On Sun, 15 Jul 2007 05:05:01 GMT, wrote:

Nope, all spread spectrum is based on discrete frequencies with
frequency hopping of some sort.

I would not consider that to be an accurate description for a variety of
direct sequence techniques, where the carrier itself is phase or
frequency modulated by a pseudorandom sequence. Such a signal, viewed on
a spectrum analyzer, looks no different than many natural, moderately
narrowband sources. And there would be nothing stopping somebody from
amplitude modulating such a signal.

Nope, mathematically AM is defined as a single carrier frequency
multipled by the modulation frequency. That you get a variation in
amplitude is an effect, not a definition.

Reference? I think you are confusing a single definition of AM with all
other definitions of the term.

I'm afraid my background IS communications so I have to say astronomers
are arm waving when they call astronomical signals AM unless ET is
phoning home.

As an astronomer, I could as easily say you are arm waving by trying to
restrict the meaning of AM to a narrow definition used within your
field. The simple fact is that astronomers _do_ refer to signals that
vary in amplitude as a function of time as "amplitude modulated". Some
of those signals are broadband, and others are not (there are, for
example, amplitude modulated natural masers). This is normal usage
within the astronomical community, and it causes no confusion at all.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

In rec.radio.amateur.space George Dishman wrote:

wrote in message
news
In rec.radio.amateur.space Chris L Peterson
wrote:
On Sun, 15 Jul 2007 03:45:01 GMT, wrote:

Spread spectrum technology uses discrete frequency hopping, not a
broad band signal as a carrier.

That is correct, it is a narrow band carrier which
moves.

That's one spread spectrum method. Not the only one. But regardless, it
still presents as a broad band carrier.

Nope, all spread spectrum is based on discrete frequencies with
frequency hopping of some sort.

Not always, consider the use of a frequency-shifted
fast PRBS as the carrier. Of course it is more
usual to use the PRBS to define the hop sequence in
the style you describe above but as you say your
background is communications, I'm sure you are aware
of the relationships between hop rate and carrier
spacing which lead to a band-limited white spectrum.

If you frequency or phase modulate, the resultant spectrum may be
quite broad, but the carrier frequency is still discreate no matter
what you modulate with.

It may look like band limited white noise on a spectrum analyser,
but if you decompose in the time domain, it isn't.

AM is a variation in amplitude of some signal- any signal- with time.

Nope, mathematically AM is defined as a single carrier frequency
multipled by the modulation frequency. That you get a variation in
amplitude is an effect, not a definition.

It is a bit of a stretch to call a signal comprised of every frequency
over a 100 GHz span AM.

Consider applying audio (with a DC bias) to a light
bulb and receiving it with a photocell. The carrier
is much more than 100 GHz wide, but I would still
call that AM, YMMV.

Got me there.

I'm afraid my background IS communications ...

Mine too ;-)

George



--
Jim Pennino

Remove .spam.sux to reply.

In rec.radio.amateur.space Chris L Peterson wrote:
On Sun, 15 Jul 2007 05:05:01 GMT, wrote:

Nope, all spread spectrum is based on discrete frequencies with
frequency hopping of some sort.

I would not consider that to be an accurate description for a variety of
direct sequence techniques, where the carrier itself is phase or
frequency modulated by a pseudorandom sequence. Such a signal, viewed on
a spectrum analyzer, looks no different than many natural, moderately
narrowband sources. And there would be nothing stopping somebody from
amplitude modulating such a signal.

If you frequency or phase modulate, the spectrum does get broad, but
there is still a discreat carrier frequency.

While it may look like band limited white noise on a vanilla spectrum
analyzer, it isn't.

Nope, mathematically AM is defined as a single carrier frequency
multipled by the modulation frequency. That you get a variation in
amplitude is an effect, not a definition.

Reference? I think you are confusing a single definition of AM with all
other definitions of the term.

How about this one:

http://www.rfcafe.com/references/ele...modulation.htm

I'm afraid my background IS communications so I have to say astronomers
are arm waving when they call astronomical signals AM unless ET is
phoning home.

As an astronomer, I could as easily say you are arm waving by trying to
restrict the meaning of AM to a narrow definition used within your
field. The simple fact is that astronomers _do_ refer to signals that
vary in amplitude as a function of time as "amplitude modulated". Some
of those signals are broadband, and others are not (there are, for
example, amplitude modulated natural masers). This is normal usage
within the astronomical community, and it causes no confusion at all.

So, is the square root of -1 j or i?


--
Jim Pennino

Remove .spam.sux to reply.

In rec.radio.amateur.space KLM wrote:


Radium wrote:

On Jul 13, 2:15 pm, wrote:
In rec.radio.amateur.space Radium wrote:

Hi:
Do magnetars emit AM radio waves below the medium-wave range? If so,
how do we detect these waves? Can these waves be heard on the AM
radio? If so, what do they sound like?

Frequencies above approximately 100 MHz almost always get through
the ionization layers.

Frequencies in the approximate range of 10 MHz to 100 MHz sometimes
get through

Frequencies below approximately 10 MHz almost never get through.

So, if by "the AM radio" you mean a Broadcast Band radio which
runs from about .5 MHz to 1.2 MHz, not a chance in hell of ever
hearing anything from off the planet.

Try again.

Okay. But what if this is a supercooled AM radio receiver on a
spaceship orbiting Earth? If I am on a space station like MIR and this
station has a supercooled AM radio 44.1 KHz frequency receiver, will I
hear anything specific of magnetars?

Nothing "specific". Thats the whole point. What exactly did you
hope to hear that you think is significant? Obviously you have
something in mind.
KLM

What makes you think there is anything in that mind other than a
bunch of technical words and terms strung together in a random manner?

--
Jim Pennino

Remove .spam.sux to reply.

On Jul 15, 3:35 am, "George Dishman" wrote:

fc fm means fc should be greater than fm, not the same.
For fm = 10,000Hz and fc = 10,001Hz you get a lower
sideband at 1Hz and an upper sideband at 20,001Hz.

Sorry. I didn't read it correctly.

If you modulate 10kHz with 10Khz, the lower sideband
becomes 0Hz or DC. The value of that depends on the
phase of the modulating signal relative to the carrier
(which is now constant since they are at the same
frequency). Of course sending DC to an antenna won't
give you a transmitted signal but it doesn't produce
an alias either.

If you modulate 10,000Hz with 10,001Hz then your lower
sideband becomes -1Hz, and of course sin(-x) = sin(x)
so that is identical to a frequency of 1Hz which you
would get if you modulated with 9,999Hz. That ambiguity
is why we call such a signal an "alias", the 10,001Hz
signal appears after modulation then demodulation
masquerading as a signal of 9,999Hz.

Does this mean an fm of 10 KHz would work on an fc of
10.0000000000000000000001 KHz?

If so, then the minimum frequency required for my "project" would be
only 20.0000000000000000001 KHz. Or just anything above 20 KHz, even
if it's just an extremely extremely small number above 20,000. Right?

I apologize if readers find my question annoying.


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